The invention generally relates to a method of producing hydrocarbons and more particularly to a single well method for specifically directed penetrations of hydrocarbon bearing formations and the removal of production-inhibiting liquids from the hydrocarbon reservoir(s) in the formations.
One of the most important and valuable resources removed from the earth are fossil fuels: such as coal, oil and gas. Since the early twentieth century, oil has become so important to the world economy that its continued supply has taken on strategic importance. To obtain fluid hydrocarbons such as oil and gas from below the earth""s surface, boreholes or well bores are drilled from one or more surface locations into hydrocarbon-bearing subterranean geological strata or formations (also referred to in the industry as the reservoirs). The hydrocarbons are then pumped from the subterranean formations, through the well bores, to the surface.
A significant proportion of the current drilling activity in the United States and other areas of the world, involves drilling highly deviated and/or substantially horizontal well bores that extend laterally through a formation. Typically, in order to drill a horizontal well bore into a desired formation, the well bore is drilled from a surface location vertically into the earth for a certain depth. At a predetermined depth, the vertical well bore is deviated into a desired direction so as to reach the desired horizontal path through the formation, which is usually the target hydrocarbon bearing formation. The horizontal portion of the well bore is then drilled a desired length into the hydrocarbon-bearing producing formation.
Horizontally drilled wells have many advantages in conventional sandstone reservoirs because of the much-improved linear flow characteristics present in horizontal wells as opposed to the radial flow characteristics inherent in vertical wells. In many different kinds of formations horizontally drilled wells have also become quite popular in attempts to produce commercially viable wells. Early work with horizontal drilling focused on formations with naturally occurring fractures such as the Austin Chalk or Bakken Shale. More recently, horizontal drilling has been applied to many other formation types.
Additionally, as described in U.S. Pat. Nos. 5,868,210 and 5,785,133, it has become very common to drill multiple lateral (laterals) well bores off from a main horizontal well bore. Those skilled in hydrocarbon recovery operations have long recognized the benefits of drilling multiple laterals off a single horizontal borehole that extends up to the surface as this drainage pattern allows for more efficient recovery of hydrocarbons from each reservoir in a formation. The primary well bore and the multi-lateral well bores are generally drilled along predetermined well bore paths that follow the various levels of producing reservoirs in any one formation.
Conventional hydrocarbon production systems leave much to be desired for a variety of reasons. One reason relates to the fact that in many gas producing formations, the targeted hydrocarbon-producing reservoir is sensitive to the presence of naturally occurring formation liquids, primarily oil and water. Methane producing subterranean formations often contain significant quantities of water, which results in high hydrostatic pressures. If the oil and water can be successfully removed from the producing reservoirs, the volume of natural gas or methane that can be produced is significantly enhanced. Typically, to provide a satisfactory methane recovery rate from a producing well bore, the region of the formation surrounding the well bore must be dewatered or drained in order to lower the hydrostatic pressure to a point where sufficient quantities of hydrocarbon gas and liquids will enter the producing well bore.
This liquid removal is achieved by reducing a producing well bore""s hydrostatic pressure in order to establish a differential pressure between the formation""s pressure and the pressure of the well bore. Once a differential pressure is established, fluid will flow from the formation into the producing well bore. The fluid in the well bore is then pumped to the surface by mechanical pumps. As the fluid in the formation is removed and the pressure in the formation is thus reduced, the methane recovery rate will increase. The removal of methane and other fluids from a recovery well that is controlled by the lowering of the pressure within the formation is generally referred to as a xe2x80x9cprimary pressure depletion methane recoveryxe2x80x9d system. Most horizontal drilling methods utilize this system of recovery.
However, pressure depletion methane recovery systems present other problems. Because of the manner in which most of the current horizontal well bore configurations are drilled, mechanical pumps are typically located in the vertical or near-vertical portion of the well bore at a substantial vertical distance above the horizontal portion of the well bore. This leads to inefficiencies in pumping the liquids from the depths of the well bore.
The method of the subject invention eliminates and/or reduces the disadvantages and problems associated with previous systems and methods. In particular, the present invention allows for a single well bore to effectively access entrained hydrocarbons and to separate down-hole non-productive fluids (water and liquid hydrocarbons) from the vaporous natural gas. This allows for a reduction in surface separation facilities. The inventive method lowers the cost of hydrocarbon production, allows for more efficient production and causes fewer disturbances to surrounding natural habitat. The use of a single well bore for the separate removal of both water and hydrocarbons allows for fewer wells to be drilled in any one formation, which minimizes the impact to the surface above the formation. The inventive method can be used for any normal or low-pressure formation including degasifying subsurface coal seams prior to mine excavation, which provides for safer coal mining conditions. It also allows for the extension of the producing life of conventional low-pressure hydrocarbon bearing formations beyond their current economic limit.
The subject invention is directed to a method for the surface recovery of hydrocarbons from a subterranean reservoir. The reservoir can be a formation found in sandstone, carbonate, coal bed or other mineral deposit formations. The method includes drilling a well bore having a first substantially vertical portion and a first substantially horizontal portion, in which the first horizontal portion intersects the subterranean reservoir. A plurality of lateral well bores intersecting and extending from the first horizontal portion of the well bore are drilled. Thereafter, a drainage well bore is drilled below and substantially parallel to the first horizontal portion of the well bore, in which the drainage well bore intersects the first horizontal portion. The drainage well bore is configured to allow for the drainage of fluids from the plurality of lateral well bores and the first horizontal portion of the well bore, which allows for the recovery of hydrocarbons through the vertical portion of the well bore separate from the fluids.
In one embodiment on the invention, the drainage well bore extends from a section of the first substantially vertical portion of the well bore at a position below the first horizontal portion of the well bore. The drainage well bore slopes downward in a first direction and then inclines upward in a second direction to intersect the first horizontal portion of the well bore. The drainage well bore is configured to allow for the drainage of fluids from the plurality of lateral well bores into the first horizontal portion of the well bore, into the drainage well bore and into the section of the vertical portion of the well bore.
In a second embodiment of the invention, the drainage well bore extends from the first horizontal portion of the well bore, at a position above a first of the plurality of lateral well bores. The drainage well bore slopes downward in a first direction and then extends outward in a second direction substantially parallel to the first horizontal portion of the well bore. The drainage well bore is configured to allow for the drainage of fluids from the plurality of lateral well bores into the first horizontal portion of the well bore, and into the drainage well bore.
In a further embodiment, a section of the vertical portion of the well bore extends a predetermined distance below the first horizontal portion of the well bore, the vertical section having a first and second side, the drainage well bore extending in a loop that originates from the first side of the vertical section, the loop thereafter intersecting the vertical section and exiting on the second side of the vertical section, the loop sloping in a first downward direction below the position of the first horizontal portion of the well bore and then inclining upward in a second direction to intersect the first horizontal portion of the well bore, the drainage, well bore being configured to allow for the drainage of fluids from the plurality of lateral well bores into the first horizontal portion of the well bore, into the drainage well bore and into the vertical section of the well bore, the lower portion of which is the last drilled.
The foregoing has outlined rather broadly the features and technical advantages of the present invention in order that the detailed description of the invention that follows may be better understood. Additional features and advantages of the invention will be described hereinafter which form the subject of the claims of the invention. It should be appreciated by those skilled in the art that the conception and specific embodiment disclosed may be readily utilized as a basis for modifying or designing other structures for carrying out the same purposes of the present invention. It should also be realized by those skilled in the art that such equivalent constructions do not depart from the spirit and scope of the invention as set forth in the appended claims. The novel features which are believed to be characteristic of the invention, both as to its organization and method of operation, together with further objects and advantages will be better understood from the following description when considered in connection with the accompanying figures. It is to be expressly understood, however, that each of the figures is provided for the purpose of illustration and description only and is not intended as a definition of the limits of the present invention.